At-sea sightings of blue whales, Balaenoptera musculus, in Brazil are rare. A mother-calf pair was observed in deep (2645 m) waters off southeastern Brazil (22°11′S 038°58′W); during a seismic survey in July 2014. It is unknown to which of the subspecies the animals sighted belong. The presence of a calf suggests that blue whales use deep waters off Brazil as calving or nursing grounds. The identification and conservation of wintering grounds for blue whale populations is important to promote the recovery of blue whales as their numbers were critically reduced as a result of commercial whaling.